The solid ink compositions disclosed herein are characterized by being solid at room temperature and molten at an elevated temperature at which the molten ink is applied to a substrate. These solid ink compositions are useful for printing inks, in particular for ink jet printing inks.
Solid ink compositions used for ink jet printing typically contain both a colorant and vehicle or carrier, where the vehicle or carrier is a material that dissolves or suspends the colorant. For example, a simple solid ink composition is composed of wax as the carrier and a pigment or dye as the colorant. Many solid ink compositions are mainly comprised of crystalline polyethylene waxes and other functionalized wax components, which allow rapid phase transitions from the molten liquid state to the solid state, and due to their low coefficient of friction, are also helpful with automated feeding of printed documents across the printer's glass platen and other subsystems. Solid ink compositions have also generally included resins as components of inks. Resins allow the ink to be sufficiently tough after cooling so that the ink is more resistant to mechanical loads on the printed substrate, such as tackiness, scratch and fold creases. Additionally, the use of resins in ink compositions has the advantage that dyes can be dissolved relatively well therein and pigments can be dispersed relatively easily therein. Resins also have the advantage that their chemical compositions can be modified readily to provide either amorphous, semi-crystalline or purely crystalline physical characteristics which contribute to solidification of the ink.
Many traditional solid ink compositions are made from highly crystalline waxes or wax-based materials, such as polyethylene waxes, and hydrocarbon amide or ester waxes, which are very hard and resistant materials that undergo rapid melting and rapid crystallization (solidification) upon cooling; however, these wax-based crystalline solid inks do experience certain physical disadvantages. For example, solid inks comprised of hard, crystalline wax-based materials are also much more brittle, so that printed matter made using such inks can be sensitive to damage by applied mechanical forces, such as for examples, scratches or cracks from page creases. In addition, crystalline wax-based solid inks generally have poor adhesion to non-porous substrates, which lends itself to poor scratch-resistance and image robustness. The highly non-polar nature of hydrocarbon waxes, such as crystalline polyethylene waxes, also can limit the solubility and miscibility of common ink components and special performance additives, such as colorants, dispersants, synergists, rheology modifiers, and antioxidants, which can result in one having to develop custom additives and materials for such inks.
As such, there is a need for alternative solid ink compositions that are not based on highly crystalline polymeric waxes that can provide durable, more robust solid ink prints without the above-described issues. There is also a need for alternative solid ink compositions that are comprised of higher polarity resins having a certain degree of both crystalline and amorphous characteristics (e.g., they have semi-crystalline properties) which would provide more viscoelasticity in the solid ink and greater compatibility with common ink additives and colorants. There is also an increasing demand for sustainable inks comprised of bio-sourced resins and components, and which may have more biodegradable functionality, compared with the commercial hydrocarbon wax-based inks.